P848: EXPRESSION PROFILE OF BCL-2 FAMILY PROTEINS IN MULTIPLE MYELOMA.
Authors: Cristina De Ramón Sánchez, Elizabeta A Rojas, Irena Misiewicz-Krzeminska, Ignacio J Cardona-Benavides, Myriam Cuadrado, Isabel Isidro, Maria Jose Calasanz, Ramón García-Sanz, Laura Rosiñol Dachs, Joaquín Martinez-Lopez, Joan Baldé, Juan J Lahuerta, Jesus F San Miguel, Maria-Victoria Mateos, Luis A Corchete, Norma Carmen Gutierrez Gutierrez
Journal: HemaSphere (2023)

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Evasion of apoptotic mechanisms due to the deregulation of Bcl-2 family proteins may play an important role in the resistance of multiple myeloma (MM) to different therapeutic schemes. Therapies targeting these proteins, such as venetoclax, which inhibits the Bcl-2 protein, have recently been developed. To date, the expression of Bcl2 family proteins in MM patients have mostly been analyzed at RNA level, even though transcript levels by themselves may not be appropriate to predict protein levels. Although, some studies analyze the expression of apoptotic proteins in MM by immunohistochemistry techniques or Western blot, the low protein concentration obtained after CD138 isolation have largely limited the quantification of proteins so far. Aims: - To investigate the expression of the Bcl-2 family proteins in newly diagnosed MM (NDMM) patients, and its association with clinical features and cytogenetic abnormalities. - To analyze the prognostic impact of Bcl-2 family proteins in NDMM patients who underwent autologous stem cell transplantation. - To explore the Bcl-2/Bcl-xl, Bcl-2/Mcl-1 and Bcl-2+Bim+Bax/Bcl-xl protein ratios, which have been associated with response to venetoclax when analyzed at RNA level, depending on the genetic alterations. Methods: Bone marrow samples from 120 NDMM patients enrolled in the Spanish Myeloma Group clinical trial GEM2012MENOS65 were included in this study. The expression of the antiapoptotic (Bcl-2, Bcl-xl, Mcl-1) and proapoptotic (Bax, Bak, Bim, Puma, and Bad) proteins were analyzed by the capillary electrophoresis nanoimmunoassay methodology (ProteinSimple, WES™ system). Results: All the Bcl-2 family proteins analyzed were expressed in more than 80% of MM patients, except Bax which was found in less than 30%. Bak, Bim and Mcl-1 were the proteins with the highest level of expression. Patients with low expression levels of Bim protein had a significant higher incidence of plasmacytomas (p = 0.019). We found that Bak protein expression was significantly higher in patients with t(14;16) (p = 0.028), while Bcl-xl and Puma expression was lower in patients with t(11;14) and 1p deletion (p = 0.014, p = 0.046), respectively. High levels of Bad and Puma proteins were associated with longer OS (p = 0.017 and p = 0.001). Conversely, high levels of Bcl-2 had a negative impact on PFS (p = 0.018).When we analyzed the values of three ratios that have demonstrated to be predictors of the response to venetoclax, we found that patients with t(11;14) had higher levels of Bcl-2/Bcl-xl and Bcl-2+Bim+Bax/Bcl-xl ratios than patients without t(11;14) [14/18 (79%) vs. 41/91 (45%), and 14/18 (79%) vs. 42/91 (46%), respectively, p = 0.01], as has been published at RNA level. Strikingly, the high Bcl-2+Bim+Bax/Bcl-xl protein expression ratio was also enriched in patients harbouring TP53 mutations compared to patients without these mutations [7/8 (87%) vs. 40/82 (49%), p = 0.036]. Summary/Conclusion: - The expression of anti and proapoptotic proteins was well-balanced in MM. - High levels of the proapoptotic proteins Bad and Puma were associated with favorable prognosis, while the overexpression of the antiapoptotic protein Bcl-2 had a negative impact on survival. - High Bcl-2/Bcl-xl and Bcl-2+Bim+Bax/Bcl-xl protein ratios were significantly enriched in patients with t(11;14). Patients harboring TP53 mutations were also significantly associated with high Bcl-2+Bim+Bax/Bcl-xl protein ratio. FUNDING: This study has been funded by ISCIII (PI19/00674) (co-funded by FEDER), Castilla y Leon (GRS 2058/A/19, GRS 2331/A/21) and AECC (PROYE20047GUTI). CDR, EAR and IJCB were supported by AECC (CLJUN18010DERA), “Consejería Educación Castilla y León” and ISCIII (FI20/00226), respectively. Keywords: Protein Expression, BCL2, Apoptosis, Multiple myeloma